The actions, if any, of the fibroblast endothelial growth factors in vivo are unknown. Naturally because they are extracted from intact organs, and especially from cells and culture, some function is likely. In cultured cells the endothelial and fibroblast growth factor family causes proliferation of fibroblast endothelial cells and smooth muscle cells and a variety of other mesenchymal cells. Because no single growth factor has been able to cause cell division, once cultured endothelial cells become confluent, one might not expect that these growth factors would have an effect in vivo, where the endothelial cell turnover rate is even slower than in the confluent cultured cell. Nevertheless, we found that in normal rats injections of large amounts of fibroblast growth factor caused endothelial cells to undergo DNA synthesis. Obviously, this may prove to be useful to enhance angiogenesis or wound healing.